Photodynamic therapy is a therapy utilizing the cell-killing capability of reactive oxygen species including singlet oxygen generated by administering a photosensitizing agent and accumulating it in an affected area, followed by light excitation. The photodynamic therapy has attracted attention in recent years because it is a noninvasive therapy less likely to leave a therapy scar. It is also known that most of compounds used as photosensitizing agents have a structure called tetrapyrrole, have absorption spectrum peaks representing characteristic strong absorbance around a wavelength of 400 nm and absorption spectrum peaks around wavelengths of 600 to 700 nm, and specifically accumulate in tumor tissue and new blood vessels. Cells of tumor tissue and new blood vessels are considered to be capable of being degenerated/necrotized by singlet oxygen produced by using light corresponding to the peak of the absorption spectrum of a photosensitizing agent as excitation light to irradiate the photosensitizing agent accumulating in tumor tissue and new blood vessels; the therapy of a disease of the skin surface such as acne by irradiation with light at a short wavelength around 400 nm and the therapy of cancer by irradiation with light at a long wavelength around 600 to 700 nm having a relatively good capability of deep tissue penetration and the like are performed (see for example, Patent Document 1).
Although 5-aminolevulinic acid (hereinafter also referred to as “ALA”) is one natural amino acid contained in a living body, broadly present in animals, plants, and fungi, ALA has no photosensitivity per se; however, protoporphyrin IX (hereinafter also referred to as “PpIX”) produced by its metabolic activation by a series of enzymes of the heme biosynthetic pathway in cells is known as a photosensitizing agent showing peaks at 410 nm, 545 nm, 580 nm, 630 nm, and the like (Non-patent Document 1), and work is proceeding on 5-aminolevulinic acid-based photodynamic therapy (hereinafter also referred to as “ALA-PDT”) which involves accumulating PpIX in cancer cells followed by irradiation with excitation light around 600 to 700 nm to degenerate/necrotize cells of an affected part (see for example, Patent Documents 2 to 9).